DC Wave Questions

To an electrical engineer, at least, DC means time invariant. I suppose DC and AC have become misnomers. For example, a sinusoidal Voltage waveform across an open circuit would be called AC even though no current flows.

And the voltage across a battery's terminals would be called DC even if there is no load, and hence no current.

If you talk to EE's, you will have to get used to them using the terms this way.

I am not sure where to set followups to, so I guess I'll just post to all four groups, and leave followups unset.

--Mac

you

communication with others.

AC-component

Ban and others are trying to educate you. You are resisting fiercely.

As I said elsewhere, DC and AC have become (or perhaps always were) misnomers. In electrical engineering circles, the terms can be applied to ANY signal, even if there is no current at all.

DC can be thought of as the average value of a waveform, or the zero frequency component, or the offset, in case of a sinewave.

Your term "DC sine wave" makes you sound ignorant of engineering terminology. If that is not a good enough reason for you to drop it, then maybe you should avoid future posts to sci.electronics.design, where many or most of the posters are electrical engineers.

--Mac

The term DC sine wave is much like Magellan still claiming the world is flat after he circumnavigated the earth.

Your wave could be a sine wave with a DC offset voltage. Or what you are calling DC might be either a step function or an impulse. DC would make the capacitors and inductors irrelevant in your original question. Your question is about L, R, and C. Therefore DC is not part of the discussion.

Now, what k> If the low peak of the sine wave (and the rest of the the sine wave for

Thank you for your comment, but I respectfully disagree....I could really care less if someone used the correct terminology in describing something, as long as I could understand what they were talking about....in fact, I run into this situation alot - I never, ever, correct the use of improper terminology (until the person is finished)....I find it to be stifling of the other person and the point they are trying to make.....thousands of times per day, people (in industry) with only high school diplomas (or less) in industry make absolutely brilliant observations and suggestions, but well over 80% of these are ignored, poo-pooed or brushed-aside, by people with advanced college degrees....many times, in part, due to the unsophisticated way in which the ideas are expressed.....it definitely is frustrating trying to understand what someone is saying when they use unfamilar or unconventional terminology, but it really can pay off big to suffer through it......

Yes, I object.

Don

No.

"There's glory for you!" "I don't know what you mean by 'glory,' " Alice said. Humpty Dumpty smiled contemptuously. "Of course you don't?till I tell you. I meant 'there's a nice knock-down argument for you!' " "But 'glory' doesn't mean 'a nice knock-down argument,' " Alice objected. "When I use a word," Humpty Dumpty said, in rather a scornful tone, "it means just what I choose it to mean?neither more nor less." "The question is, " said Alice, "whether you can make words mean so many different things." "The question is," said Humpty Dumpty. "which is to be master?that's all."

--
Regards,
  Bob Monsen

I assume that you are meaning that you have 10vpp wave with 10vdc offset. The answer is the latter, but the terminology that you are using is incorrect. It is not all dc. It IS a varying current with a dc component. The impedance must account for all factors.

Leonard

misunderstand you

On the other hand, given a sheet of paper with a drawing of your waveform on it, I don't think too many readers would have described it as "a fully DC sine wave".

Another irritating newbie habit you have is replying without keeping at least a pip of the message to which you are replying.

Ignorance, be not proud.

Nobody interrupted your first post; that's the one of the beauties of usenet. You get to have your say without interruption. Nobody tried to correct your improper use of terminology until you were well finished with your first post.

And is it characteristic of these people that when somebody freely offers to help them learn to express their ideas better, they react as you have here? Strongly resisting and refusing to learn?

How much more might it pay off if the person using the unfamiliar terminology learns the conventions?

And, it certainly hasn't paid off big here. The majority of your postings have been argument about terminology, rather than attempts to get your questions answered.

You came to this newsgroup seeking instruction in electronics, an area where you apparently lack extensive training. Your question # 1 is ill-posed, and when you were offered instruction, you resisted with vociferous arrogance. There is a considerable body of knowledge about electricity, with a standard terminology. Why should we who would instruct you use your sui generis terminology rather than you use the standard language? Part of answering such an ill-posed question is teaching the proper way to ask, which the qroup was willing to do, but you want to bite the hand that feeds you.

jackbruce9--

Dis thing dat yu gots with da "DC Sine Wave" speak'n make no cents to dis cat.

Tut

("DC sine wave")....

Just because someone else used the term doesn't make it right ! There's plenty of rubbish spouted on the net.

Graham

Indeed - depending on the configuration of the R, L, C combination there may no DC component *at all* and the current would be purely a.c.

Graham

Try a simple experiment. Build a simple oscillator powered off of two 9V batteries ie +/- 9V.

Now measure the output. with the scopes gnd probe on the point between the two batteries, and again with the gnd probe at either exterme of the batteries.

In the first case you will measure a signal that oscilates around 0, in the other two cases it will be entirely above or below 0. The wave has not changed. It would make absolutely no sense to describe it in one case as AC and in the others as DC. As much to the point describing as DC would make understanding it more difficult.

Just as there is no absolute inertial reference frame, there is no absolute voltage reference.

Robert

The output of a rectifier contains both AC and DC. You put a filter on it to get close to pure DC.

Rectified AC _is_ DC. Now you might say, But it has a lot of AC stuff riding on it and that makes it "rectified AC."

Okay, so let's hang a large capacitor across the rectifier's output. Now, assuming there is some sort of load connected to the rectifier, there will still be ripple on the load--so there is still some AC present. Is this still rectified AC? Using your definition, when does the signal change from rectified AC to DC?

As long as there is a finite load on the rectifier that I've described, anything less than infinite capacitance will permit some ripple to be present. So, since you say "... When a waveform varies with time, it is NOT DC in popular useage," then the signal will never become DC.

The simple truth is that a current flowing in only one direction is, by definition, direct current. It might have AC riding on it, but if it's direction doesn't change, it's DC.

Yes, I would object. You can't predict that without knowing the whole circuit. Connect your DC sine wave to a reactance and current (and energy) will indeed flow in both directions.

jackbruce9--

You're getting a variety of answers because your input source shape is vague--because of the terminology--let me try to help, you pick whats best for your "DC sine wave."

1.Nonsinusoidal, nonperiodic source + RCL circuit--difficult to analyze--requires calculus, Fourier analysis, and Lapace transforms

2.Nonsinusoidal periodic source + RCL circuit--difficult to analyze--requires calculus and Fourier series

3.Sinusoidal source + RCL-- fairly easy to analyze--requires some work with complex numbers

4.DC source + RCL--not so easy to analyze--requires calculus and differential equations to understand what's really going over time

5.DC source + resistor only circuit--easy to analyze with algebra and ohms law, Kirkoff etc.

So there you have it.

Good luck

Tut